Problems in the laboratory diagnosis of alcaptonuria.

Two patients with urinary findings suggestive of alcaptonuria were observed. One was a two-year-old girl of Turkish descent, presenting with dark-stained diapers, black ear wax, and no other stated problem. The second was a 61-year-old North American Indian woman with long-standing rheumatoid arthritis, bluish sclerae, chronic renal failure, and dark urine. Diagnosis of alcaptonuria was confirmed in the first case by paper chromatographic identification of homogentisic acid in urine and ear wax; also a small amount of a substance with R1 similar to that of homogentisic acid was found in urine of the patient’s mother and brother. Whether this implies possibilities for heterozygote detection requires further study. Gentisic acid, a phenolic acid metabolite of acetylsalicylic acid, was responsible for the dark color of the urine in the second patient. This latter finding has not been emphasized in this context, and may cause confusion when patients with arthritis and pigmentation are investigated for possible alcaptonuna.